The present invention relates generally to rotating electrical machines and, more particularly, to a fan for a rotating electrical machine.
The increasing demand for electrical power in automotive vehicles has driven advances in alternators (generators) for electrical power. As the components of electrical machines are heated, the electrical machines lose efficiency. Electrical machines commonly use fans in order to cool the machines and improve performance. These fans typically have blades supported at the base of the blades. Unfortunately, recently developed electrical machines require increasingly higher cooling rates such that the resulting increase in fan speed subjects the blades to centrifugal forces that commonly cause the blades to fracture. Since the tips of the blades are left unsupported, the centrifugal forces associated with the high speed rotation may fatigue the blades to the point of fracture by repeatedly bending the blades back and forth about their bases.
Currently, a typical alternator uses two fans, each comprising a round disk having an outer edge with rectangular blades extending perpendicularly therefrom. Ordinarily, the blades are only supported at their bases. These blades are disposed at a predetermined angle relative to a radial line of the disk. A bottom surface of the disk is fixedly coupled to a top surface of a rotor. A top surface of the disk is exposed to freely circulating air. The disk typically has a center opening with a rotatable shaft fixedly coupled thereto. The shaft has a longitudinal axis about which the fan rotates.
In operation, the fan typically draws air in a first direction parallel to the longitudinal axis of the shaft. The air flows from a space above the top surface of the disk into a center area of the fan. More specifically, air flows from an external space of the alternator through vent openings of the housing into the center area of the fan. Once inside the housing, the air cools the alternator. Then, the heated air is drawn in a second direction radially outward relative to the disk. The heated air typically flows from the center area of the fan across the top surface of the disk to the blades. Once the heated air reaches the blades, the blades may direct the heated air to flow along two general paths. On a first path, the blades direct the heated air in a third direction radially outward relative to the disk. The heated air may flow across an outer surface of the blades in a substantially radial direction with respect to the disk and exit the alternator through vent openings in the housing. Alternatively, on a second path, the blades may direct the heated air in a third direction parallel to the longitudinal axis of the shaft. The heated air flows across the outer surface of the blades away from the top surface of the disk. The heated air flows into the space above the top surface of the disk.
One disadvantage of the fan is that heated air which flows along the second path may fail to properly exit the alternator. The second path can direct the heated air into the space above the top surface of the disk. Because of the fluid nature of air, the heated air may be recirculated into the alternator as the fan draws air from the space above the top surface of the disk in the first direction. Another disadvantage of the fan is the fatigue fracture of blades resulting from the centrifugal forces associated with high rotational speed.
Known designs for preventing blade fracture include conventional fans using large gussets, thicker material, higher strength metal, or plastic material. However, the disadvantages of these fans can include limited success, higher costs, and manufacturing and packaging difficulty.
It would therefore be desirable to provide a fan for an electrical machine that can operate under high centrifugal forces without fatigue fracture and improve the cooling of the alternator to increase performance.
It is therefore one object to provide a fan for an electrical machine that provides increased support for each blade to prevent fracture thereof.
It is a further object of the present invention to provide a fan for an electrical machine that improves cooling by improving air circulation about the electrical machine.
In one aspect of the invention, a fan comprises a continuous ring, a plurality of blades, and a plurality of tabs. The continuous ring is disposed in a top plane and connects the plurality of blades extending therefrom. The plurality of tabs extends from the plurality of blades into a bottom plane so as to be parallel to the continuous ring disposed in the top plane. The plurality of tabs is preferably laser welded to a pole of the rotor.
One advantage of the invention is that the continuous ring and the plurality of tabs support the plurality of blades so as to allow the fan to operate at high rotational speeds without experiencing fatigue fracture. Another advantage is that the continuous ring directs the flow of heated air so as to improve circulation about the electrical machine and performance of the machine.